The known drive arrangement (DE 10 2008 057 014 A1) on which the invention is based is equipped with two electrical spindle drives which each have a drive motor. In order to counteract any uneven wear of the two drives that are embodied in an identical manner, a control device ensures that the two drive motors are supplied with an identical amount of drive power.
The control device acts upon the two drive motors with a pulse width modulation voltage (“PWM” voltage) in order to be able to ensure as low as possible a power loss when controlling the rotational speed or torque of the drive motors. In the case of the PWM power control of consumers, in this case drive motors, the problem quite generally arises that interfering harmonic waves are formed, the frequency of which regularly amounts to many times the switching frequency of the respective PWM voltage. This can be particularly problematic with respect to the electromagnetic compatibility (EMC).
U.S. Pat. No. 6,433,507 B1 discloses one approach for reducing EMC interference when controlling the PWM power. This document proposes to continuously vary the duty cycle, in other words the ratio of high duration time to low duration time of a PWM pulse, during the motor-operated adjustment. As a consequence, the above-mentioned interference is reduced in a simple manner.